Abstract: Compounds of Formula 1, and pharmaceutically acceptable forms thereof, are provided: wherein the variables X, Y, Z, A1, R2, R3, R4, R5 and R6 are defined herein. Certain compounds of Formula 1 described herein which possess potent antiviral activity. Certain compounds of Formula 1 that are potent and/or selective inhibitors of Hepatitis C virus replication. Pharmaceutical compositions containing one or more compounds of Formula 1, or a salt, solvate, or acylated prodrug of such compounds, and one or more pharmaceutically acceptable carriers, excipients, or diluents are also provided. Methods of treating patients suffering from certain infectious diseases by administering to such patients an amount of a compound of Formula 1 effective to reduce signs or symptoms of the disease or disorder are disclosed. These infectious diseases include viral infections, particularly HCV infections.